HUMAN PHYSIOLOGY: INTRODUCTION 



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fore depends upon its composition or the amounts and kinds 

 of nutrients present. It must contain one or more of the 

 following substances, proteids, carbohydrates, fats, water 

 and inorganic salts. 



The following table shows approximately the average com- 

 position of some of those substances commonly used as food. 



Composition of Foods.* 



♦Howell's Physiology, p. 676 (with slight additions). 



Uses of nutrients (proteids, carbohydrates, fats, salts, 

 and water). — The exact use of each kind of nutrient to the 

 body is a subject upon which there has been much careful 

 experimentation. Two things are positively known, and 

 they have already been stated. First, the nutrients furnish 

 the cells with materials for growth and metabolism, and 



